The present invention relates to a variable displacement compressor. More specifically, the present invention pertains to a controller for controlling the inclination of a swash plate in a variable displacement compressor.
Japanese Examined Patent Publication No. 2-9188 describes a swash plate type variable displacement compressor. The compressor includes a swash plate and pistons. The swash plate, which is located in a crank case (pressure control chamber), integrally moves with a drive shaft and inclines with respect to the drive shaft. The strokes of the pistons vary in accordance with the inclination of the swash plate. When the pressure in the crankcase is relatively high, the inclination of the swash plate is small, which causes the compressor to operate at a small displacement. When the pressure in the crankcase is relatively low, the inclination of the swash plate is large, which causes the compressor to operate at a large displacement. Adjusting the pressure in the crankcase controls the displacement of the compressor. It is important to determine a precise minimum inclination position of the swash plate and to precisely control the inclination of the swash plate. In the compressor described in Publication 2-9188, the swash plate is located between two springs, that is, a displacement restoration spring and an inclination reduction spring. The restoration spring is located between a snap ring fixed on the drive shaft and a hinge ball supporting the swash plate on the drive shaft. The restoration spring continuously contacts the hinge ball and urges the swash plate to incline. The restoration spring increases the inclination of the swash plate from the minimum inclination position and helps restore the displacement. The restoration spring also precisely determines the minimum inclination position of the swash plate, which reduces power consumption.
To maintain a certain minimum inclination of the swash plate, the minimum inclination is determined by the minimum length of the restoration spring (the length when fully compressed). The longer the restoration spring is when uncompressed, the longer it is when compressed. Therefore, the uncompressed length of the restoration spring also determines the distance between the hinge ball and the snap ring at the minimum inclination position of the swash plate. In other words, the longer the uncompressed length of the restoration spring is, the greater the distance between the hinge ball and the snap spring at the minimum inclination position becomes, which increases the axial length of the compressor.
To reduce the distance between the hinge ball and the snap spring at the minimum inclination position, the characteristic of the restoration spring may be changed. For example, the length of the spring may be reduced and the spring may be hardened. However, if the length of the restoration spring is less than the distance between the hinge ball and the snap ring at the maximum inclination, the spring moves along the drive shaft, which may cause noise and damage the compressor.